Sharif Digital Repository

Surface-Piercing Propellers (SPPs) are essential categories of high-performance propulsion systems usually used for high-speed boats, which are designed to operate in semi-submerged conditions. In such conditions, a propeller performs in a two-phase mixed environment, consisting of water and air concurrently. Due to the intrinsic complexity of the working environment, describing the performance of an SPP is complex and cannot be recognized with the traditional submerged propellers. The present study aims to assess the effect of immersion depth on semi-submersible propellers. Accordingly, experimental tests in a towing tank were used along with a numerical method to achieve reliable results.... 

Abstract: Bead-on-plate submerged arc welding was conducted on St37 steel by manufactured Cr, Mo, and Cr–Mo active basic fluxes produced via the unfused bonded method. The base metal heat-affected zone and weld metal (WM) microstructures were identified and characterized by optical microscopy and scanning electron microscopy. Furthermore, each element’s recovery rate (η) and slag factor (α) determine the amount of element transferred from flux into WM. Then, the ferrite morphologies volume fraction of WMs was measured. Moreover, the chemical analysis of slag and inclusions was evaluated by point scan energy-dispersive X-ray spectroscopy and extensively discussed. The number density and... 

Although concrete armour units have traditionally been used in two layers, the application of single-layer armour has attracted more attention in recent years because of its lower concrete volume and faster construction pace. Single-layer amour relies mainly on the contact between units to provide stability; however, installation of special armour types with surface projections for better interlocking, increases the possibility of breakage. During the last decade the idea of using bulky armour units such as cubes has been raised, and the application of these single-layer armour units has become common for high-crested breakwaters. However, the application of cube armours for low-crested... 

The hydro-acoustic analysis of submerged propellers is an important issue in marine industries, which is examined to reduce the vibrations and noise level of vessels alongside reducing fuel consumption and improving hydrodynamic efficiency. B-series propellers are common propellers whose hydrodynamic and acoustic investigation through applying suitable rake, and skew angle can offer proper results to designers for enhancing the hydrodynamic performance and reducing noise. In this study, a model of the five-bladed B-series propeller with the normal skew angle is chosen. The effects of geometric parameters, including the rake angle, skew angle, geometric pitch ratio, and the number of blades... 

Bead-on-plate submerged arc welding was performed on the AISI 4135 heat-treatable low-alloy (HTLA) steel using S2 welding wire and granular Cr-Mo basic flux. The Cr-Mo active flux was produced by the bonded -unfused method. The alloying elements were introduced into the weld metal by active flux. Two methods were introduced for calculating the recovery rate (η) of the alloying elements. Moreover, by defining the slag factor (α) of the process and η of the alloying elements, the amount of a specific element transferred from flux into WM was calculated by the proposed equation. Likewise, microstructure evolutions, inclusions characteristics, longitudinal tensile, indentation, and CVN impact... 

Bead-on-plate submerged arc welding was performed on the AISI 4135 heat-treatable low-alloy (HTLA) steel using S2 welding wire and granular Cr-Mo basic flux. The Cr-Mo active flux was produced by the bonded -unfused method. The alloying elements were introduced into the weld metal by active flux. Two methods were introduced for calculating the recovery rate (η) of the alloying elements. Moreover, by defining the slag factor (α) of the process and η of the alloying elements, the amount of a specific element transferred from flux into WM was calculated by the proposed equation. Likewise, microstructure evolutions, inclusions characteristics, longitudinal tensile, indentation, and CVN impact... 

This paper represents a numerical study on the effects of landslide initial submergence and its geotechnical and rheological properties on the characteristics of landslide-generated waves (LGWs) and landslide deformation. A number of 117 numerical experiments are performed using a two-layer Coulomb Mixture Flow (2LCMFlow) model on a real-sized numerical flume as a simplified cross section of the Maku dam reservoir, located in the Northwest of Iran. Three different initial locations are considered for landslide representing a subaerial (SAL), a semi-submerged (SSL), and a submarine (SML) landslide. Based on the numerical results, the majority of SMLs and in some cases SSLs generate tsunami... 

Abstract This article studies a submerged membrane electro-bioreactor (SMEBR), an integrated system embracing biological treatment, electrical coagulation, and membrane filtration, all in one individual reactor, by applying an alternating electric field to a membrane bioreactor (MBR). The alternating electric field has been applied with current densities ranging from 5 to 23 A/m2 under eight different electrical exposure modes. The results indicate that under the optimum condition with a current density of 12.5 A/m2 and an exposure mode of (415 s OFF-185 s ON), the COD and phosphate removals would be respectively 4% and 43% more compared to an unmodified MBR system. Also at the same current... 

The ability of Paraconiothyrium variabile, a laccase producing ascomycete recently isolated from soil, was studied to eliminate chlorophenol derivatives in submerged culture medium. Among the tested compounds, ρ-chlorophenol (ρ-CP) and pentachlorophenol (PCP) were found to have minimum and maximum toxic effects, respectively, on the growth of the microorganism and at the same time high and low bioelimination percentages. The fungal strain was able to remove 86% of ρ-CP (with initial concentration of 40mgl -1) and 56% of 2,4-dichlorophenol (2,4-DCP; with same concentration as ρ-CP) after 9 days of incubation while no elimination was observed in the presence of 2,4,6-trichlorophenol... 

The hydraulic performances of drain pipes are very important in drainage projects and systems. Usually these pipes are used in a saturated soil to decrease the water table to a favorable level or, drain the excess water. However, drain pipes can be used in a water or wastewater tank for different purposes such as selective withdrawal. There are not much published documents on the performance of drain pipes in submerged situations. Therefore, the aim of this study was to examine the performance of drain pipe in a submerged tank. For this, a horizontal pipe of 26.5 mm inner diameter, 5 meter long with 48 circular drain inlets of 10 mm diameter at equal distances along the pipe have been tested... 

A comprehensive set of experiments was performed on weirs placed obliquely in a rectangular open channel. The main objectives were to investigate the effect of the weir angle relative to the approach flow direction on the behaviour and the hydraulic flow characteristics and to examine methods such as using upstream guide vanes and inclined aprons to increase the effective oblique weir length. Results indicate that by increasing the oblique angle, the effective length of the oblique weir increases significantly. Relationships are provided for the threshold submergence and the effective length of the oblique weir. Design recommendations are also presented for the use of guide vanes and... 

ZnO nanostructures were synthesized through arc discharge of zinc electrodes in deionized (DI) water. X-ray diffraction (XRD) analysis of the prepared nanostructures indicates formation of crystalline ZnO of hexagonal lattice structures. Transmission electron microscopy (TEM) images illustrate rod-like as well as semi spherical ZnO nanoparticles with 15-20 nm diameter range, which were formed during the discharge process with 5 A arc current. The average particle size was found to increase with the increasing arc current. X-ray photoelectron spectroscopy (XPS) analysis confirms formation of ZnO at the surface of the nanoparticles. Surface area of the sample prepared at 5 A arc current,... 

Production yield of solid-state (SSF) and submerged fermentation (SMF) on chitosan from Aspergillus niger was investigated. A. niger BBRC 20004 was grown on soybean residue and Sabouraud Dextrose Broth medium (2% glucose). Chitosan was extracted from the fungal mycelia using hot alkaline and acid treatment. Soybean residue at a moisture content of 37%, and 8-4 ± 0.26% of nitrogen content produced the highest amount of chitosan, 17.053 ± 0.95 g/kg dry substrate after 12 days. Also, chitosan was extracted from A. niger on Sabouraud Dextrose Broth medium in submerged fermentation (0.8455 g/l after 12 days of cultivation). The yield of chitosan isolated in SSF was about 15-20 times more than in... 

Airlift pumps are devices with the ability to lift liquid phase by injecting the gas phase. Parameters that affect the performance of these pumps are divided into two groups. The first group contains design parameters such as diameter of the pipe, tapering angle of the upriser pipe, and the submergence ratio, which is the ratio of immersed length to the total length of the upriser. The second group includes operating parameters such as the gas flow rate, bubble diameter, bubble distribution, and inlet gas pressure. In this research, the performance of an airlift pump is investigated numerically for different submergence ratios and different diameter of the upriser pipe. For this purpose, an... 

The objective of this investigation was to provide a detailed evaluation of the heat affected zone properties of a high-strength pipeline steel. The X80 high-strength low-alloy microalloyed steel was supplied as a hot rolled plate with accelerated cooling. The four-wire tandem submerged arc welding process with different heat input was used to generate welded joints. The microstructure of the heat affected zone depended on heat input values. M/A constituent appeared in the microstructure of HAZ region for all of the specimens along the prior-austenite grain boundaries and between bainitic ferrite laths. Charpy impact specimens were notched in four locations: FL (fusion line), FL+1mm, FL+2mm... 

The objective of this paper is to study the influence of the second peak temperature during real and simulated welding on properties of the subcritically (S), intercritically (IC) and supercritically (SC) reheated coarse grained heat affected (CGHAZ) zones. The X80 high strength pipeline microalloyed steel was subject to processing in a double-pass tandem submerged arc welding process with total heat input of 6.98 kJ/mm and thermal cycles to simulate microstructure of reheated CGHAZ zones. This involved heating to a first peak temperature (TP1) of 1400 °C, then reheating to different second peak temperatures (TP2) of 700, 800 and 900 °C with a constant cooling rate of 3.75 °C/s. Toughness of... 

One of the sources of disturbance at intakes is the occurrence of free-surface vortices with an air core. The most common solution for avoiding air-entrainment is the use of anti-vortex devices and, especially, plates for large pipe or shaft intakes. If plates are used, then, the geometry and position of them should be studied experimentally. Since only general guidance for use of plates is available, a study for the more precise placement of plates is needed. Hence, a comprehensive set of experiments have been carried out using rectangular plates with different dimensions and at various positions with respect to the vertical outlet pipe intakes and two different pipe diameters (D = 75 and... 

Two phase lifting pumps are devices with the ability of lifting liquid phase by injecting the gas phase. Parameters which affect the performance of these pumps are divided into two groups. The first group contains design parameters such as diameter of the pipe, tapering angle of the upriser pipe and the submergence ratio which is the ratio of immersed length to the total length of the upriser. The second group includes operating parameters, such as the gas flow rate, bubble diameter, bubble distribution and inlet gas pressure. In this research, the performance of two phase lifting pump is investigated numerically for different submergence ratios and different diameter of the upriser pipe.... 

Surface and submerged fermentation methods were used to produce citric acid by Aspergillus niger using chemically defined media or cane molasses. Fermentation process parameters were optimized in pilot scale tower and tray fermenters. Fermentation was running from 10 - 20 days with pH controlled at 3 - 6.5. Citric acid concentrations varied from 60 - 100 g/L depending on the strain used, the substrate, the fermentation system and the general conditions under which fermentation took place (initial sugar concentration, aeration rate, inoculum size, pH and temperature). Some essential criteria such as lower process sensitivity to short interruptions or breakdowns in aeration, expenses for... 

The effect of glucose concentration in submerged fermentation (SMF) on chitosan production by Aspergillus niger was investigated. A. niger, BBRC, 20004, from the Biochemical and Bioenvironmental Research Centre at Sharif University of Technology, Tehran, Iran, was grown in a Sabouro Dextrose media. Chitosan was extracted from the fungal mycelia using hot alkaline and acid treatment and after 12 days of cultivation, 0.8455 g chitosan /l of the fermentation medium was obtained. The content of glucose in the Sobouro Dextrose Broth media was also changed and the highest yield of chitosan 0.9121 g/l was obtained in Sobouro Dextrose Broth media containing 8% glucose. © Sharif University of...